They said that they charge in two tiers, by the amount recovered.
Tier 1 is the stuff you don't really NEED back. Your OS, desktop pictures, application installations, etc. Things you can reinstall yourself.
Tier 2 is the important things. Email. Do ents. Spreadsheets. Databases. Those are charged much higher by the MB.
This prevents you from having to pay a fortune to recover a 300kb xls spreadsheet that you have to have back, that is on a more or less empty HD with an OS X installation on it.
A typical recovery on a 80gb'ish HD is between $500 and $2900, depending on the data recovered. They apparently have an excellent success rate.